Method of jet plating



Sept. 30, 1958 E. M. ZIMMERMAN METHOD OF JET PLATING Filed Nov. 21, 1955 to form the deposit.

- of the jet plating orifice,

Mnrnon or nr PLATING Elizabeth M, Zimmerman,-'Shar0n-I-lill, Pa., assignor to PhilcoCorporation,Philadelphimla a corporation of Pennsylvania Application November '21, 1955, Serial No. 548,090

18 Claims. (Cl.' 204-15) The present invention relates-to a novel method of jet plating; and, more particularly, the present invention relates to a novelmethod of jet plating whereby aplated recently developed method of jet plating of a small deposit onto a semiconductive material forms the subject matter of copending application Serial No. 472,824, filed December 3, 1954. In jet plating, electrolyte. containing a-saltof the metal to be deposited is forced through a jet orificein a direction normal to the plane of the surface onto which the metal is to=be plated whereby it 'impingesthe surface at the point at which it is desired The material onto which the deposit is plated is the cathode, and the jet device is the anode of the system.

One of the presently most prevalent uses of jet plating is in the manufacture of surface barrier transistors and'high frequency junction transistors. The manufacture of such transistors involves providing a pair of opposed, closely confronting potential barriers, serving as icollector and emitter respectively, in a small, thin wafer of semi-conductive material. Providing these potential barriers involves application of a relatively minute body or dot of an appropriate metal to the semi-conductive base wafer. Where a high frequency junction device is desired the resulting assembly is heated to alloy thetwo materials together at their interface and then cooled to cause recrystallization of the semi-conductive material.

The present invention is particularly adapted to the initial application of the relatively minute dot of metal to the base wafer by means of jet platingv Before jet plating the dots, however, the base wafer is preferably provided with closely-spaced'apart, parallel depressions on the opposite faces so that the applied metal dots providing the potential barriers will be as close together as possible. These depressions areformed by jet etching,

' that is by directing a stream of electrolytic etching solution normal to each of the broad surfaces of the wafer and completing the electrical circuit'between the streams and the wafer whereby the wafer is the anode and the jet device the cathode. The area of the pit or depression is determined by the area of the jet orifice, the area of the depression being normally on the same order as or slightly larger than that of the jet orifice. After the desired depressions have been etched into the base wafer, the relatively minute dot of appropriate metal is then plated at the bottom of the depressions. In transistors of the type described, however, it is desirable that the plated dot be sufficiently smaller than the etched pit or depression that it will be limited substantially to the relatively flat bottom portion of the depression. Since, under normal conditions, the size of the dot plated is comparable or in some cases even larger than the area the provision of a dot of the required smaller size has required, in the past, either a Unite 11 States Patent separate set of smaller jet orifices or use ofthe'same' jet orifices used during jet etching followed=by etching=of the resulting plated dotto reduce its dimensionsltothe desired size. .Each ofthese procedures-possesses--disadvantages not only from'the standpointof-;-the-number of steps, the additional :equipment and timerequired, but also, in thedifliculty of preparing satisfactory and readily reproducible products.

It is known thatthesame electrolyte -solution-.canbe employed injet platingasin jet etching. For example, a solution of zinc sulfateand sulfuric acid in water can be employed for jet-plating--zinc and the verysametsolution can be employedfor jetetching, requiringonly a reversal'in direction-of current to convert fromietching to plating. It will beseen, therefore, that thezprovision of means whereby the same jet system, including jetoriice ' fices, can be used in both the jet platingtand jet-etching jet'system,

the jet plating operation .as was employed during" 'the jet etchingoperation with the provision, however, of a plated operations to provide, directly as thenresult of, jet plating, a deposit of a size/smaller than the depression formed during the jet etching operation wouldbe highlydesirable.

It is the principal object of the presentiinvention to Another object of the invention is to provide a method of jet plating wherein, the size of the depositimayl-be readily controlled to a desiredsize less than thatofthe jet orificebysimple varation in the current employed.

' A specific object of thepresentinvention is to provide a method of jet plating metal dots in the. manufacture of transistors ofthe types-described whereby the same including jet' orifice, can be employedduring depositsmaller in; size than the depression formed during the jet etching operation.

Other objects willbecome. apparent from a consideration'of the followingspecification and claims.

The method of the" present invention involves, in the metal l' deposit 'onto another surface ,by directing a stream of electrolyte comprising an. aqueous solution of salt'of the'metal to'be deposited.against' the surface onto whichthe deposit is to be appliedlandcompleting the'circuit between'the jet device andthe surface throughthe electrolyte stream whereby the said surface isthecathode and the jet device is'thefanodeinlthe system, the improvement which comprises "conducting such-plating with a polar organic compound "selected from the group consisting of water-soluble :e'thersfketones and"hydro yl-freeamines dissolved in said electro- 'lyte' wherebythe plated deposit has a cross-sectional'arca less than-that of the jet orifice.

""Thepresent method will be morereadily understood from aconsiderationof-the drawings in which:

Figure 1 illustrates, in greatly enlarged section, the

* jet etching 'ofdepressionsin-opposite sides of, a'base jet plating,-

Water, and

"Figure 2 lllllSlI'fllI6S,'lll greatly enlarged sectionfithe of a '"dotof metalin each or the-depressions formed during the jet etching operation ofFigure 1 and using the same jet systemas inFigure l.

lthasbeen foundlthat, by including in solution in the electrolyte plating bath polar organic compounds'from the classes setforth above, the current can be'sharply' reduced fron'i'that normally employed in jet plating to provide a deposit having a cross-section comparable'tothat of the jet orifice with the result-that a deposit of "metal will form that is much sm'allerin cross-sectional area than the cross-section of the jet drificeemployed. Moreover, it has been found, that withthe inclusion ofFthe stated 1 additives in the ielectrolyte solution, simple voltage control permits the deposit size to be varied at will from a specific embodiment,

about $4; to about A the jet diameter. The reason for the foregoing is not presently understood, although it is believed that, by virtue of the presence of the described additive, the potential at the center of the jet stream is sharply increased over that at the periphery of the stream near the surface'of the wafe The electrolyte solution selectively plates only when and where the ionic decomposition potential is reached at the surface of the base wafer. Hence, selective deposition occurs at the center of the stream.

At any rate, the present invention results in a high quality metal deposit smaller than the jet orifice employed, and hence smaller than that which would normally result without the use of the stated additives. In the invention permits. the use, during jet plating in the manufacture of transistors, of the same jet system, including jet orifices, employed during jet etching the desired depressions with assurance, however, that the deposit of metal as the direct result of plating will be smaller in size than the jet orifice opening and hence, smaller than the area of the depression formed during jet etching. Thus, there need be no changeover from one jet system or orifice to another between etching and plating, and there need be no interruption in the etching and plating procedure, only a reversal of the flow of current being necessary to discontinue etching and initiate plating, since, as stated previously, the same electrolyte solution can be employed in both etching and plating. Nor need there be any subsequent etching to reduce the size of the metal deposit to that required in the assembly. The present procedure permits the entire operation from initial etching through plating to be carried out in a single machine, in very short periods of time, on the order of seconds or minutes, and eliminates the handling time, labor and capital investment involved in the operation of separate machines. Because the size of deposit can be controlled electrically by means of the present procedure, the jet plating apparatus can be arranged to provide, by simple electrical adjustments, a wide variety of deposit sizes less than that of the jet orifice.

The base onto which the metal is electrodeposited in accordance with the present method may be any solid material that can be electroplated by conventional means. Such materials embrace any solid material that will conduct electricity to an appreciable degree, such as metals and semi-conductive materials like germanium, silicon, magnesium oxide, lead sulfide, intermetallic compounds, like tellerides, antimonides and arsenides, and the like. Since the present method is particularly applicable for the preparation of potential barriers of the type described, the base will most generally be semi-conductive material, especially silicon or germanium.

The electrolyte solution employed in the jet etching procedure of the present invention will comprise, in addition to the constituents normally used in such procedure, at least one of the additives of the type described herein. Such solutions normally comprise an aqueous solution of a salt of the metal to be deposited. The solution may be acid or alkaline, although acid solutions are preferred. Salts significantly soluble in water will be selected, such as the sulfates, chlorides, nitrates, and the like, with the sulfates being preferred. The salt employed will have a cation corresponding to the metal to be deposited, and these may vary widely depending upon the particular use desired for the product. Zinc, indium, nickel, cadmium, and the like, are examples of metals that may be deposited by the present procedure. The concentration of the metal salt in the electrolyte solution may vary widely. Generally, 'as the concentration increases the size of the deposit increases, and this tendency may serve as a means of controlling the size of the deposit along with the additive which has the opposite effect. In some cases the concentration of metal salt can go as high as about 10%, by weight, althoughnormally it will be relatively low, a concentration between about 1% and about 5 by weight, being particularly suitable.

The present invention is not concerned with the absolute size of the metal deposit, since this may vary widely depending upon the particular type of product desired. In general, however, the jet plating procedure may be employed to provide deposits ranging in size from about 1-2 mils to as high as about .5 inch in diameter. As stated, the present procedure is particularly applicable to the preparation of potential barriers in the manufacture of transistors in which case the diameter of the deposit may range from'about l to about 20 mils, preferably between about 2 and about 10 mils particularly in the case of potential barriers for high frequency junction transistors.

As stated, the electrolyte solution is preferably acidic in nature, and with salts of most of the metals to be plated, the pH will be below about 3.5 to avoid precipitation. The pH may go as low as about 1. In accordance with preferred practice, the electrolyte solution will have a pH between about 2 and about 3. The desired acid pH may be readily provided by including in the bath a suitable acid, preferably a mineral acid such as sulfuric acid, hydrochloric acid, nitric acid, or the like. In accordance with preferred practice, the anion of the acid selected will correspond to that of the metal salt.

'For example, when zinc sulfate is the metal salt employed, sulfuric acid is the preferred acid selected to provide the desired pH. With some plating systems, however, such as cyanide solution, alkaline baths are employed, having a pH above about 8.5, preferably between about 9 and about 10. Appropriate alkaline materials may be used to provide the desired high pH in such case.

The success of the present procedure depends upon the inclusion in the electrolyte solution of a water-soluble polar organic compound selected from certain classes of such compounds. Extensive research has lead to the belief that any of the. water-soluble ethers, ketones or hydroxyl-free amines may be employed. So far as the ethers are concerned, those selected may range from the simple alkyl ethers, such as diethyl ether, to the cyclic ethers, such as dioxane. Of the ethers, the glycol ethers are preferred, and these may be selected from a wide variety of such materials including the water-soluble alkyl and aryl ethers of the alkylene and polyalkylene glycols, such as the monomethyl ether of ethylene glycol, the monoethyl ether of ethylene glycol, the monobutyl ether of ethylene glycol, the monomethyl ether of diethylene glycol, the monoethyl ether of diethylene glycol, the monobutyl ether of diethylene glycol, the monomethyl ether of triethylene glycol, the monoethyl ether of triethylene glycol, the monomethyl ether of propylene glycol, the monoethyl ether of propylene glycol, the monomethyl ether of dipropylene glycol, the monoethyl ether of dipropylene glycol, the monomethyl ether of tripropylene glycol, the monoethyl ether of tripropylene glycol, the diethyl ether of ethylene glycol, the diethyl ether of diethylene glycol, the benzyl ether of ethylene glycol, the 2,4-dichlorophenyl ether of propylene glycol, and the like. To provide significant results, the ethers should be soluble in water at least to the extent of about 2%, by volume, and, with the glycol ethers specifically best re sults are obtained with those soluble in water at least to the extent of about 7%, by volume. The glycol ethers of the type described represent one of the preferred groups employed in accordance with the present invention. One of the other preferred classes constitutes the water-soluble, hydroxyl-free amines, that is amines that contain no OH group substituent, and these may be selected from a wide variety of such materials including the primary alkyl amines, such as ethyl amine; the secondary alkyl amines, such as diethyl amine; the aryl amines, such as aniline and its derivatives, the heterocyclic tertiary amines, for instance pyridine, and its derivatives, morpholine and its derivatives, and the like. To provide signifiassess? cant results the amine should be soluble in water to the the aromatic compounds.

The amount of polar organic compound employed may vary over a wide range of concentrations, although optimum results may be obtained for any particular compound at diiferent concentration levels as indicated above. In general, the amount of polar organic compound employed may vary from as low as about 1% to as high as about 50%, by volume.

As far as the temperature of the bath is concerned during the plating operation, no advantage is to be gained by employing temperatures substantially in excess of room temperature, and, in fact, with excessive temperatures the throwing power of the bath may be increased resulting in unsatisfactory deposits. In general, the temperature of the bath during the plating operation may range between about and about 50 C., with a preferred temperature being in the neighborhood of about -25 C.

Through the inclusion of one of the stated polar organic compounds in the electrolyte solution in accordance with the present invention, the current employed during jet plating may be substantially reduced from that normally employed in providing a deposit comparable in size to that of the jet orifice. As stated, the current may also be controlled to provide a deposit having any desired size less than that of the jet orifice from about /8 to about Vs the size thereof. This reduction in-current from that normally employed without the inclusion of the polar organic compound is not a simple linear function, since, for example, a reduction in current density to about A of that normally required may provide a deposit about one-half the size of the jet orifice. The exact current employed in practicing the present invention will depend not only upon the desired size of deposit but also upon the metal being deposited and the additive selected and hence the makeup of the electrolyte system. Thus, it is not possible to set forth any numerical ranges within which any desired deposit size may be obtained for any desired metal using any desired additive. However, no difficulty will be experienced by one skilled in the art in determining the proper current for any selected set of conditions and materials. As an example, indepositing zinc from a solution containing zinc sulfate, sulfuric acid and the monoethyl ether of ethylene glycol, the current density may be about 2.6 amperes per square foot to provide a deposit one-half the size of the jet orifice whereas a current density of 22 amperes per square foot is normally required to provide a deposit of zinc comparable in size to'that of the same jet orifice without the use of the monoethyl ether of ethylene glycol.

Referring to the drawings, Figure 1 represents, in greatly enlarged cross-section, a view of jet etching as used in the preparation of junction and surface barrier transistors. In the embodiment illustrated, pits or depressions are being etched into base wafer 1. The depressions are of different sizes, the larger depression for the collector and the smaller depression for the emitter. 2 represents the electrolyte solution flowing from the respective jet orifices 3 and 4. As illustrated in the drawing the electrolyte solution is forced through the respective orifices in a direction normal to the plane of the base wafer 1 so that each stream impinges at the point at which it is desired to etch into the base. Not shown inthe drawing are the conventional means for holding the base 1 between jet orifices 3 and 4 and for control- 6 ling the distance between the orifices and the surface. of the base wafer, as well as the overall jet mechanism including reservoirs for electrolyte solution, filters, valves, air pressure connections and electrical connections.

In Figure 2 is illustrated the-jet plating of metal deposits at the bottom of the depressions etched in accordance with Figure l and employing the same electrolyte solution and mechanism as employedin Figure 1. In this case, the base 1, electrolyte solution 2 and jet orifices 3 and 4 are the same as described in Figure 1, the only difference being that the flow of current is reversed with respect to that employed during'etching in Figure 1. During plating as illustrated in Figure 2, a depositof the desired metal forms at the bottom of the depression, the deposit in the collector depression being designated 5, and the deposit at the bottom of the emitter depression being designated 6. As shown in the drawing the size of the deposit is substantially less than that of the respective jet orifice.

The method of the present invention will be more readily understood from a consideration of the following specific examples which are given for the purpose of illustration only and are not intended to limit the scope of the invention in any way.

Example I A strip of germanium isground to a thickness of 7 mils and cut on a cavitron into discs 90 mils in diameter. These discs are then etched in a bath containing nitric acid, acetic acid, hydrofluoric acid and bromine to a thickness of 2 mils, and this reduces the diameter to approximately 75 mils.

The resulting blank is then mounted horizontally between two opposed jets having orifice diameters of 5 and '8 mils, respectively, the smaller jet being directed upwardly and the larger jet being directed downwardly upon the blank. Each jet is provided with its own solu tion reservoir, valve, electrode, filter and air pressure connection. Positive and negative power supplies are provided for etching and plating. Plating and etching currents are controlled by series potentiometers and monitored by 02 ma. meters.

The electrolyte solution employed, both for etching and for plating, is prepared by dissolving 25 grams of zinc sulfate, 3 cc. of concentrated sulfuric acid and 250 cc. of monoethyl ether of ethylene glycol in 1 liter of water. The temperature of the bath is 20 C.

The blank is first etched to provide two pits the bottoms of which are .03 mil apart, and the diameters of the pits are 9 and 12 mils, respectively. This takes about 30 seconds. During etching the current applied at the upper jet is 1.5 milliamperes and the current applied at the bottom jet is 1 milliampere.

When the desired pits have been provided in the blank, the current is reversed to begin plating zinc deposits in each of the pits. Employing a plating current of .04 milliampere in the top jet and .02 milliampere in the bottom jet produces zinc deposits of 2 and 4 mils in diameter, respectively, in 15 seconds.

Example I] In this example the procedure of Example I is-followed except that the jet etching and jet plating electrolyte is prepared by dissolving 20.5 grams of indium sulfate, 3 cc. of concentrated sulfuric acid and 250 cc. of of the monoethyl ether of ethylene glycol in one literof water, and the plating current is 0.14 milliampere in the top jet, and 0.1 milliampere in the bottom jet.

Indium metal deposits of 2 and 4 mils diameter are formed in the top and bottom pits, respectively.

Example III In this example the procedure of Example I is followed except that the jet etching and jet plating electrolyte is prepared by dissolving 25 grams of zinc sulfate, cc. of diethylamine and 7 cc. of concentrated sulfuric acid in one liter of water, and the plating current is 0.3 milliampere in the top jet and 0.21 milliampere in the bottom jet. The electrolyte has a pH of 3.

Zinc metal deposits of 2 and 4 mils in diameter are formed in the top and bottom pits, respectively.

Example IV In this example the general procedure of Example I is followed with an electrolyte prepared by dissolving grams of zinc sulfate, 2.5 of aniline sulfate and suflicient concentrated sulfuric acid in one liter of Water to provide a pH of 3.5. The deposits of zinc are of the same size as in the preceding examples.

Example VI In this example the general procedure of Example I is followed with an electrolyte prepared by dissolving 25 grams of zinc sulfate, 100 cc. of 1,4-dioxane and sufficient concentrated sulfuric acid in one liter of water to provide a pH of 2.5. The deposits of zinc are of the same size as in the preceding examples.

Example VII In this example the general procedure of Example I is followed with an electrolyte prepared by dissolving 25 grams of zinc sulfate, 100 cc. of acetone and suflicient concentrated sulfuric acid in one liter of water to provide a pH of 2.5. The deposits of zinc are of the same size as in the preceding examples.

Example VIII In this example the same general procedure of Example I is followed with an electrolyte preparedby dissolving 25 grams of zinc sulfate, 15 cc. of methyl ethyl ketone and 2.5 cc. of concentrated sulfuric acid in one liter of water to provide a pH of 2.5. The deposits of zinc are of the same size as in the preceding examples.

Example IX In this example the same general procedure of Example I is followed with an electrolyte prepared by dissolving 25 grams of zinc sulfate and 2.5 grams of pyridine hydrochloride in one liter of water. The deposits of zinc are of the same size as in the preceding examples.

Example X In this example the same general procedure of Example I is followed with an electrolyte prepared by dissolving 25 grams of zinc sulfate, 100 cc. of diethyl ether and sutficient concentrated sulfuric acid in one liter of water to provide a pH of 2.5. The deposits of zinc are of the same size as in the preceding examples.

Example XI In this example the general procedure of Example I is followed with an electrolyte prepared by dissolving 25 grams of zinc sulfate, 60 cc. of the methyl ether of tripropylene glycol and sufiicient concentrated sulfuric acid in one liter of water to provide a pH of 2.5. The deposits of zinc are the same size as in the preceding examples.

Example XII In this example the general procedure of Example I is followed with an electrolyte prepared by dissolving 25 grams of zinc sulfate, 20 cc. of the 2,4-dichlorophenyl ether of propylene glycol and sutficient concentrated sulfuric acid in one liter of water to provide a pH of 2.5. The deposits of zinc are the same size as in the preceding examples.

Considerable modification is possible in the selection of polar organic compound and other constitutents of the electrolyte bath as well as in the amounts thereof and in the conditions and techniques employed without departing from the scope of the invention.

I claim:

1. In the jet plating of a metal deposit onto another surface involving directing a stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited against the surface onto which the deposit is to be applied and completing the circuit between the jet device and the surface through the electrolyte stream whereby the said surface is the cathode and the jet device is the anode in the system, the improvement which comprises conducting such plating with a water-soluble ether dissolved in said electrolyte at a current density whereby the plated deposit has a cross-sectional area less than that of the jet orifice.

2. The method of claim 1 wherein the ether is a glycol ether.

3. In the jet plating of a metal deposit onto another surface involving directing a stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited against the surface onto which the deposit is to be applied and completing the circuit between the jet device and the surface through the electrolyte stream whereby the said surface is the cathode and the jet device is the anode in the system, the improvement which comprises conducting such plating with a water-soluble ketone dissolved in said electrolyte at a current density whereby the plated deposit has a cross-sectional area less than that of the jet orifice.

4. In the jet plating of a metal deposit onto another surface involving directing a stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited against the surface onto which the deposit is to be applied and completing the circuit between the jet device and the surface through the electrolyte stream whereby the said surface is the cathode and the jet device is the anode in the system, the improvement which comprises conducting such plating with a water-soluble hydroxyl-free amine dissolved in said electrolyte at a current density whereby the plated deposit has a crosssectional area less than that of the jet orifice.

5. The method of claim 4 wherein the amine is morpholine.

6. The method of claim 4 wherein the amine is pyridine.

7. The method of claim 4 wherein the amine is aniline.

8. The method of claim 1 wherein the said plated deposit has a cross-sectional area of from about to about M: of that of the jet orifice.

9. The method of claim 8 wherein the concentration of said ether in said electrolyte is at least about 2% by volume.

10. The method of claim 8 wherein said ether is a glycol ether and is present in a concentration of at least about 7% by volume.

11. The method of claim 3 wherein said ketone is present in said electrolyte in a concentration of at least about 1% by volume and said plated deposit has a crosssectional area of from about to about M1 of that of the jet orifice.

. 12. The method of claim 4 wherein said amine is present in a concentration of at least about 1% by volume and said plated deposit has a cross-sectional area of from about to about A; of that of the jet orifice.

13. In the jet plating of a metal deposit onto another surface involving jet etching a depression in said surface and then directing a stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited against the surface at the site of the depression and completing the circuit between the jet device and the surface through the electrolyte stream whereby the said surface is the cathode and the jet device is the anode in the system, the improvement which comprises conducting said jet etching and said jet plating with said electrolyte having dissolved therein a water-soluble ether and,'without interrupting the flow of electrolyte, reversing the flow of current to discontinue etching and to initiate plating at a current density whereby the plated deposit has a cross-sectional area less than that of the jet orifice.

14. In the jet plating of a metal deposit onto another surface involving jet etching a depression in said surface and then directing a stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited against the surface at the site of the depression and completing the circuit between the jet device and the surface through the electrolyte stream whereby the said surface is the cathode and the jet device is the anode in the system, the improvement which comprises conducting said jet etching and said jet plating with said electrolyte having dissolved therein a water-soluble ketone and, without interrupting the flow of electrolyte, reversing the flow of current to discontinue etching and to initiate plating at a current density whereby the plated deposit has a cross-sectional area less than that of the jet orifice.

15. In the jet plating of a metal deposit onto another surface involving jet etching a depression in said surface and then directing a. stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited against the surface at the site of the depression and completing the circuit between the jet device and the surface through the electrolyte stream whereby the said surface is the cathode and the jet device is the anode in the system, the improvement which comprises conducting said jet etching and said jet plating with said electrolyte having dissolved therein a water-soluble hydroxyl-free amine and, without interrupting the flow of electrolyte, reversing the flow of current to discontinue etching and to initiate plating at a current density whereby the plated deposit has a cross-sectional area less than that of the jet orifice.

16. In the fabrication of potential barriers in the manufacture of surface barrier or high frequency junction transistors involving jet etching depressions into opposite faces of a wafer of semi-conductive material and jet plating a small deposit of metal in said depressions by directing a stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited at each depression and completing the circuit between the jet device and the semi-conductive material through the electrolyte stream whereby the semi-conductive material is the cathode and the jet device the anode in the system,

the improvement which comprises conducting said jet etching and said jet plating with said electrolyte having dissolved therein a water-soluble ether and, without interrupting the flow of electrolyte, reversing the flow of current to discontinue etching and to initiate plating at a current density whereby the plated deposit has a crosssectional area less than that of the jet orifice.

17. In the fabrication of potential barriers in the manufacture of surface barrier or high frequency junction transistors involving jet etching depressions into opposite faces of a wafer of semi-conductive material and jet plating a small deposit of metal in said depressions by directing a stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited at each depression and completing the circuit between the jet device and the semi-conductive material through the electrolyte stream whereby the semi-conductive material is the cathode and the et device the anode in the system, the improvement which comprises conducting said jet etching and said jet plating with said electrolyte having dissolved therein a water-soluble ketone and, without interrupting the flow of electrolyte, reversing the flow of current to discontinue etching and to initiate plating at a current density whereby the plated deposit has a cross-sectional area less than that of the jet orifice.

18. In the fabrication of potential barriers in the manufacture of surface barrier or high frequency junction transistors involving jet etching depressions into opposite faces of a wafer of semi-conductive material and jet plating a small deposit of metal in said depressions by directing a stream of electrolyte comprising an aqueous solution of salt of the metal to be deposited at each depression and completing the circuit between the jet device and the semi-conductive material through the electrolyte stream whereby the semi-conductive material is the cathode and the jet device the anode in the system, the improvement which comprises conducting said jet etching and said jet plating with said electrolyte having dissolved therein a water soluble hydroxyl-free amine and, without interrupting the flow of electrolyte, reversing the flow of current to discontinue etching and to initiate plating at a current density whereby the plated deposit has a cross-sectional area less than that of the jet orifice.

References Cited in the file of this patent UNITED STATES PATENTS 1,416,929 Bailey May 23, 1922 2,355,505 Bray et a1. Aug. 8, 1944 2,384,300 Hartford Sept. 4, 1945 2,751,341 Smart June 19, 1956 2,765,516 Haegele Oct. 9, 1956 OTHER REFERENCES Proceedings of the I. R. E., vol. 41, No. 12, December 1953, Tiley et al., pp. 1706-1708. 

1. IN THE JET PLATING OF A METAL DEPOSIT ONTO ANOTHER SURFACE INVOLVING DIRECTING A STREAM OF ELECTROLYTE COMPRISING AN AQUEOUS SOLUTION OF SALT OF THE METAL TO BE DEPOSITED AGAINST THE SURFACE ONTO WHICH THE DEPOSIT IS TO BE APPLIED AND COMPLETING THE CIRCUIT BETWEEN THE JET DEVICE AND THE SURFACE THROUGH THE ELECTROLYTE STREAM WHEREBY THE SAID SURFACE IS THE CATHODE AND THE JET DEVICE IS THE ANODE IN THE SYSTEM, THE IMPROVEMENT WHICH COMPRISES CONDUCTING SUCH PLATING WITH A WATER-SOLUBLE ETHER DISSOLVED IN SAID ELECTROLYTE AT A CURRENT DENSITY WHEREBY THE PLATED DEPOSIT HAS A CROSS-SECTIONAL AREA LESS THAN THAT OF THE JET ORIFICE. 